Check for your sprocket at http://www.alibaba.com/  Search for "ladder
chain sprockets".  Most likely they have a sprocket that can be used,
or the hub altered to fit your needs.  They also will make sprockets
out of either metal or a variety of plastics.  Their website says that
in most cases they can produce as few as one, but some sprockets have
a 10-piece minimum order.  This may be a less expensive route than
having the sprocket made by 3-D printing.

Al Good
Waynesboro, Pennsylvania